Among phosphate-based positive electrode materials, LiVOPO4 has been known as a compound that can achieve a charging/discharging voltage as high as 4 V. However, a lithium ion secondary battery with LiVOPO4 has not yet achieved sufficient reversible capacity or rate characteristic. The above positive electrode material is disclosed in, for example, Patent Documents 1 and 2 and Non-Patent Documents 1 to 4 below. It is known that lithium ions can reversibly intercalate into and deintercalated from the crystal represented by the structural formula LiVOPO4.